linux-kernel - [PATCH for 4.4] powerpc: Fix incorrect stw{, ux, u, x} instructions in __set_pte

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Message-Id: <7aff7043c9212bfd495af42931d61f45f86c7137.1610521433.git.christophe.leroy@csgroup.eu>
Date:   Wed, 13 Jan 2021 07:12:43 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH for 4.4] powerpc: Fix incorrect stw{, ux, u, x} instructions in
 __set_pte_at

From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Backport for 4.4

(cherry picked from commit d85be8a49e733dcd23674aa6202870d54bf5600d)

The placeholder for instruction selection should use the second
argument's operand, which is %1, not %0. This could generate incorrect
assembly code if the memory addressing of operand %0 is a different
form from that of operand %1.

Also remove the %Un placeholder because having %Un placeholders
for two operands which are based on the same local var (ptep) doesn't
make much sense. By the way, it doesn't change the current behaviour
because "<>" constraint is missing for the associated "=m".

[chleroy: revised commit log iaw segher's comments and removed %U0]

Fixes: 9bf2b5cdc5fe ("powerpc: Fixes for CONFIG_PTE_64BIT for SMP support")
Cc: <stable@...r.kernel.org> # v2.6.28+
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Acked-by: Segher Boessenkool <segher@...nel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/96354bd77977a6a933fe9020da57629007fdb920.1603358942.git.christophe.leroy@csgroup.eu
---
 arch/powerpc/include/asm/pgtable.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index b64b4212b71f..408f9e1fa24a 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -149,9 +149,9 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 		flush_hash_entry(mm, ptep, addr);
 #endif
 	__asm__ __volatile__("\
-		stw%U0%X0 %2,%0\n\
+		stw%X0 %2,%0\n\
 		eieio\n\
-		stw%U0%X0 %L2,%1"
+		stw%X1 %L2,%1"
 	: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
 	: "r" (pte) : "memory");
 
-- 
2.25.0